1. Field of the Invention
The present invention relates to a print head driving circuit for driving a print head having a plurality of nozzles.
2. Description of the Related Art
Conventionally, in an inkjet printer, a print head drive voltage waveform generating circuit and drive voltage waveform generating method have been proposed, with the object of obtaining a desired waveform, in a programmable fashion, by means of a simple operation. In these proposals, data for a plurality of points in a plurality of drive voltage waveforms at a prescribed temperature are previously stored as absolute coordinate data, and the data for a plurality of points in a desired drive voltage waveform are read out on the basis of tonal gradation data, and the data for this plurality of points is corrected on the basis of the difference between the ambient temperature during printing and the aforementioned prescribed temperature. Thereupon, the corrected absolute coordinate data is converted to relative coordinate data, and values between the points are interpolated, the interpolated drive voltage waveform data is converted to an analogue signal, and then amplified and output (see Japanese Patent Laid-open No. (Hei)11-20203, for example.)
In the conventional print head driving circuit 51 shown in FIG. 1, the voltage signal from the drive waveform generating circuit 53 is input to a current amplifying circuit 54 constituted by connecting an NPN type transistor 54a and a PNP type transistor 54b (hereinafter, both of these elements are called “transistor”), in a push-pull configuration. By amplifying the current of the aforementioned voltage signal, the voltage signal output from the current amplifying circuit 54 is supplied, as a nozzle driving voltage, to one electrode 52a of any one of the piezo elements provided respectively on each of the nozzles of the print head, via a switching circuit 55, which forms a transmission gate (for the sake of simplicity, only the piezo element labeled 52 is illustrated).
However, if the drive rate of any one of the aforementioned nozzles (piezo elements 52), which is the load of the current amplifying circuit 54 declines suddenly, for example, then a transient response will occur consequently in the operation of the transistor 54a. Therefore, cases may occur where the base voltage of the transistor 54a rises in excess of the prescribed value, giving rise to distortion in the nozzle drive voltage waveform output by the current amplifying circuit 54. In an inkjet printer provided with a print head driving circuit as illustrated in FIG. 1, if waveform distortion such as that described above occurs in the nozzle drive voltage, in other words, if the accuracy of the nozzle drive voltage waveform falls, then this risks causing a decline in printing quality. For example, if, in the middle of simultaneously performing printing using cyan ink and printing using magenta ink, for example, the printer changes suddenly from a state of solid printing of cyan ink to a state where no cyan ink is to be printed, then there is a risk that color fluctuation will occur in the printing using magenta ink.